Method for producing GaN crystal

ABSTRACT

The present invention provides a novel method for producing a GaN crystal, the method including growing GaN from vapor phase on a semi-polar or non-polar GaN surface using GaCl3 and NH3 as raw materials. Provided herein is an invention of a method for producing a GaN crystal, including the steps of: (i) preparing a GaN seed crystal having a non-polar or semi-polar surface whose normal direction forms an angle of 85° or more and less than 170° with a [0001] direction of the GaN seed crystal; and (ii) growing GaN from vapor phase on a surface including the non-polar or semi-polar surface of the GaN seed crystal using GaCl3 and NH3 as raw materials.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Application No.PCT/JP2017/007451, filed on Feb. 27, 2017, and designated the U.S., andclaims priority from Japanese Patent Application 2016-050395 filed onMar. 15, 2016, Japanese Patent Application 2016-173103 which was filedon Sep. 5, 2016, Japanese Patent Application 2016-173104 which was filedon Sep. 5, 2016, and Japanese Patent Application 2016-187698 which wasfiled on Sep. 27, 2016, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates mainly to a method for producing a GaN(gallium nitride) crystal.

BACKGROUND ART

A method using GaCl₃ (gallium trichloride) as a Ga (Gallium) source invapor phase growth of a GaN crystal has been proposed for some time.

Gaseous GaCl₃ can be generated by vaporizing solid GaCl₃ (PatentDocument 1).

It has been shown that gaseous GaCl₃ having higher purity can beobtained by reacting metal Ga and Cl₂ (chlorine gas) with each other toproduce GaCl (gallium monochloride) and further reacting the producedGaCl with Cl₂ (Patent Documents 2 and 3).

Patent Document 2 describes an experimental result where growth of GaNfrom vapor phase was achieved on a sapphire (0001) substrate using GaCl₃and NH₃ (ammonia) as raw materials; however, the orientation of the GaNcrystal grown is unclear.

Patent Document 3 describes an experimental result where growth of GaNfrom vapor phase was achieved on a GaN (000-1) substrate using GaCl₃ andNH₃ as raw materials.

To the best of the present inventors' knowledge, no one has hithertotried to grow GaN on a non-polar or semi-polar GaN surface using GaCl₃as a raw material.

PRIOR ART DOCUMENT Patent Documents

Patent Document 1: WO2007/143743

Patent Document 2: WO2011/142402

Patent Document 3: WO2015/037232

SUMMARY OF INVENTION Problem to be Solved by Invention

A main object of the present invention is to provide a novel method forproducing a GaN crystal, the method including growing GaN from vaporphase on a semi-polar or non-polar GaN surface using GaCl₃ and NH₃ asraw materials. The object of the present invention includes providing anovel method for producing a GaN crystal, the method including growingGaN from vapor phase using GaCl₃ and NH₃ as raw materials.

Solution to Problem

The present inventors tried to grow GaN from vapor phase on a non-polaror semi-polar GaN surface using GaCl₃ and NH₃ as raw materials andthereby found out that when the non-polar or semi-polar GaN surface hasa particular orientation, GaN is growable thereon. One aspect of thepresent invention was made based on such findings.

Embodiments of the present invention include the following.

(1) A method for producing a GaN crystal, comprising: (i) a seed crystalpreparation step of preparing a GaN seed crystal having a non-polar orsemi-polar surface whose normal direction forms an angle of 850 or moreand less than 1700 with a [0001] direction of the GaN seed crystal; and(ii) a growth step of growing GaN from vapor phase on a surfacecomprising the non-polar or semi-polar surface of the GaN seed crystalusing GaCl₃ and NH₃ as raw materials.

(2) The method for producing a GaN crystal according to (1) above,wherein the angle formed by the normal direction of the non-polar orsemi-polar surface with the [0001] direction of the GaN seed crystal is85° or more and less than 90°, 90° or more and less than 93°, 93° ormore and less than 97°, 97° or more and less than 102°, 102° or more andless than 107°, 107° or more and less than 112°, 112° or more and lessthan 122°, or 122° or more and less than 132°.

(3) The method for producing a GaN crystal according to (1) or (2)above, wherein the angle formed by the normal direction of the non-polaror semi-polar surface with the [0001] direction of the GaN seed crystalis 87° or less or 930 or more.

(4) The method for producing a GaN crystal according to any one of (1)to (3) above, wherein in the growth step, GaN is grown on the non-polaror semi-polar surface at a growth rate of 1 μm/h or more.

(5) The method for producing a GaN crystal according to (4) above,wherein the growth rate is 50 μm/h or more.

(6) The method for producing a GaN crystal according to (4) or (5)above, wherein the growth rate is less than 150 μm/h.

(7) The method for producing a GaN crystal according to any one of (1)to (4) above, wherein in the growth step, GaCl₃ is supplied to the GaNseed crystal at a partial pressure of 1.5×10⁻³ atm or more.

(8) The method for producing a GaN crystal according to any one of (1)to (4) and (7) above, wherein in the growth step, a product of partialpressures of GaCl₃ and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵atm² or more.

(9) The method for producing a GaN crystal according to any one of (1)to (8) above, wherein an intersection line between the non-polar orsemi-polar surface and a C-plane of the GaN seed crystal extends in ana-axis direction ±150.

(10) The method for producing a GaN crystal according to (9) above,wherein the intersection line extends in an a-axis direction ±30.

(11) The method for producing a GaN crystal according to any one of (1)to (10) above, wherein a low-index orientation of the GaN seed crystalparallel or nearest parallel to the normal of the non-polar orsemi-polar surface is <10-10>, <30-3-1>, <20-2-1>, <30-3-2>, or<10-1-1>.

(12) The method for producing a GaN crystal according to any one of (1)to (11) above, wherein the GaN seed crystal is at least part of a GaNsubstrate, and the non-polar or semi-polar surface is a main surface ofthe GaN substrate.

(13) The method for producing a GaN crystal according to (12) above,wherein the GaN substrate is a GaN single crystal substrate.

(14) The method for producing a GaN crystal according to (12) above,wherein the GaN substrate is a template substrate comprising a basesubstrate and a GaN single crystal layer grown on the base substrate.

(15) The method for producing a GaN crystal according to (12) above,wherein the GaN substrate is a GaN layer-bonded substrate comprising abase substrate and a GaN single crystal layer bonded to the basesubstrate.

(16) The method for producing a GaN crystal according to any one of (12)to (15) above, wherein in the growth step, a bulk GaN crystal having amaximum growth height of 300 μm or more on the non-polar or semi-polarsurface is grown.

(17) The method for producing a GaN crystal according to (16) above,wherein the maximum growth height of the bulk GaN crystal is 300 μm ormore and less than 500 μm, 500 μm or more and less than 1 mm, 1 mm ormore and less than 3 mm, 3 mm or more and less than 5 mm, 5 mm or moreand less than 10 mm, 10 mm or more and less than 25 mm, 25 mm or moreand less than 50 mm, 50 mm or more and less than 75 mm, 75 mm or moreand less than 100 mm, or 100 mm or more and less than 200 mm.

(18) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN seed crystal having one ormore facets selected from a {10-10} facet and a {10-1-1} facet; and (ii)a growth step of growing GaN from vapor phase on a surface comprisingthe one or more facets of the GaN seed crystal using GaCl₃ and NH₃ asraw materials.

(19) The method for producing a GaN crystal according to (18) above,wherein in the GaN seed crystal, a ratio of a size in a direction of ac-axis to a size in an arbitrary direction perpendicular to the c-axisis not less than 0.1 and not more than 10.

(20) The method for producing a GaN crystal according to (18) or (19)above, wherein each of the one or more facets is an as-grown surface.

(21) The method for producing a GaN crystal according to any one of (18)to (20) above, wherein the GaN seed crystal further has a (000-1) facet.

(22) The method for producing a GaN crystal according to (21) above,wherein in the growth step, GaN is also grown on the (000-1) facet.

(23) The method for producing a GaN crystal according to any one of (18)to (22) above, wherein in the growth step, GaN is grown on each of theone or more facets at a growth rate of 1 μm/h or more.

(24) The method for producing a GaN crystal according to (23) above,wherein the growth rate is 50 μm/h or more.

(25) The method for producing a GaN crystal according to (23) or (24)above, wherein the growth rate is less than 150 μm/h.

(26) The method for producing a GaN crystal according to any one of (18)to (23) above, wherein in the growth step, GaCl₃ is supplied to the GaNseed crystal at a partial pressure of 1.5×10⁻³ atm or more.

(27) The method for producing a GaN crystal according to any one of (18)to (23) and (26) above, wherein in the growth step, a product of partialpressures of GaCl₃ and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵atm² or more.

(28) The method for producing a GaN crystal according to any one of (1)to (27) above, wherein in the growth step, growth of GaN is repeatedintermittently.

(29) The method for producing a GaN crystal according to any one of (1)to (28) above, wherein the GaCl₃ is generated by reacting metal Ga andCl₂ with each other to produce GaCl and reacting the produced GaCl withCl₂.

(30) The method for producing a GaN crystal according to any one of (1)to (29) above, wherein in the growth step, GaN is grown at a growthtemperature of 1200° C. or more.

(31) A method for producing a GaN wafer, comprising: a crystalproduction step of producing a GaN crystal by the method for producing aGaN crystal according to any one of (1) to (30) above; and a crystalprocessing step of processing the GaN crystal produced in the crystalproduction step to form at least one GaN wafer.

(32) The method for producing a GaN wafer according to (31) above,wherein the GaN wafer formed in the crystal processing step includes aGaN wafer selected from a {10-10} wafer, a {30-3-1} wafer, a {20-2-1}wafer, a {30-3-2} wafer, a {10-1-1} wafer, a {30-31} wafer, a {20-21}wafer, a {30-32} wafer, a {10-11} wafer, a (0001) wafer, and a (000-1)wafer.

(33) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN wafer as a seed crystal, theGaN wafer being a {20-2-1} wafer; and (ii) a growth step of growing GaNfrom vapor phase on the GaN wafer using GaCl₃ and NH₃ as raw materials.

(34) The method for producing a GaN crystal according to (33) above,wherein in the growth step, GaN is grown at a growth rate of 1 μm/h ormore.

(35) The method for producing a GaN crystal according to (34) above,wherein the growth rate is 1 μm/h or more and less than 50 μm/h, 50 μm/hor more and less than 100 μm/h, or 100 μm/h or more and less than 150μm/h.

(36) The method for producing a GaN crystal according to (33) or (34)above, wherein in the growth step, GaCl₃ is supplied to the GaN wafer ata partial pressure of 1.5×10⁻³ atm or more.

(37) The method for producing a GaN crystal according to (33), (34) or(36) above, wherein in the growth step, a product of partial pressuresof GaCl₃ and NH₃ supplied to the GaN wafer is 9.5×10⁻⁵ atm² or more.

(38) The method for producing a GaN crystal according to any one of (33)to (37) above, wherein in the growth step, a GaN crystal comprising aportion where an FWHM of a (201) plane X-ray rocking curve is less than100 arcsec is formed on the GaN wafer.

(39) The method for producing a GaN crystal according to any one of (33)to (38) above, wherein the GaCl₃ is generated by reacting metal Ga andCl₂ with each other to produce GaCl and reacting the produced GaCl withCl₂.

(40) The method for producing a GaN crystal according to any one of (33)to (39) above, wherein in the growth step, GaN is grown at a growthtemperature of 1200° C. or more.

(41) A method for producing a GaN wafer, comprising: producing a GaNcrystal by the method for producing a GaN crystal according to any oneof (33) to (40) above; and subsequently processing the produced GaNcrystal to form a GaN {20-21} wafer.

(42) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN wafer, the GaN wafer being a{10-10} wafer; and (ii) a growth step of growing GaN from vapor phase onthe GaN wafer using GaCl₃ and NH₃ as raw materials.

(43) The method for producing a GaN crystal according to (42) above,wherein in the growth step, GaN is grown at a growth rate of 1 μm/h ormore.

(44) The method for producing a GaN crystal according to (43) above,wherein the growth rate is 1 μm/h or more and less than 50 μm/h, 50 μm/hor more and less than 100 μm/h, or 100 μm/h or more and less than 150μm/h.

(45) The method for producing a GaN crystal according to (42) or (43)above, wherein in the growth step, GaCl₃ is supplied to the GaN wafer ata partial pressure of 1.5×10⁻³ atm or more.

(46) The method for producing a GaN crystal according to (42), (43) or(45) above, wherein in the growth step, a product of partial pressuresof GaCl₃ and NH₃ supplied to the GaN wafer is 9.5×10⁻⁵ atm² or more.

(47) The method for producing a GaN crystal according to any one of (42)to (46) above, wherein in the growth step, a GaN crystal comprising aportion where an FWHM of a (100) plane X-ray rocking curve is less than100 arcsec is formed on the GaN wafer.

(48) The method for producing a GaN crystal according to any one of (42)to (47) above, wherein the GaCl₃ is generated by reacting metal Ga andCl₂ with each other to produce GaCl and reacting the produced GaCl withCl₂.

(49) The method for producing a GaN crystal according to any one of (42)to (48) above, wherein in the growth step, GaN is grown at a growthtemperature of 1200° C. or more.

(50) A method for producing a GaN wafer, comprising: producing a GaNcrystal by the method for producing a GaN crystal according to any oneof (42) to (49) above; and subsequently processing the produced GaNcrystal to form a GaN {10-10} wafer.

(51) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN seed crystal having a{10-10} surface; and (ii) a growth step of growing GaN from vapor phaseon the {10-10} surface using GaCl₃ and NH₃ as raw materials.

(52) The method for producing a GaN crystal according to (51) above,wherein in the growth step, GaN is grown on the {10-10} surface at agrowth rate of 1 μm/h or more.

(53) The method for producing a GaN crystal according to (52) above,wherein the growth rate is 1 μm/h or more and less than 50 μm/h, 50 μm/hor more and less than 100 μm/h, or 100 μm/h or more and less than 150μm/h.

(54) The method for producing a GaN crystal according to (51) or (52)above, wherein in the growth step, GaCl₃ is supplied to the GaN seedcrystal at a partial pressure of 1.5×10⁻³ atm or more.

(55) The method for producing a GaN crystal according to (51), (52) or(54) above, wherein in the growth step, a product of partial pressuresof GaCl₃ and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵ atm² ormore.

(56) The method for producing a GaN crystal according to any one of (51)to (55) above, wherein in the growth step, a GaN crystal comprising aportion where an FWHM of a (100) plane X-ray rocking curve is less than100 arcsec is formed on the {10-10} surface.

(57) The method for producing a GaN crystal according to any one of (51)to (56) above, wherein the GaCl₃ is generated by reacting metal Ga andCl₂ with each other to produce GaCl and reacting the produced GaCl withCl₂.

(58) The method for producing a GaN crystal according to any one of (51)to (57) above, wherein in the growth step, GaN is grown at a growthtemperature of 1200° C. or more.

(59) A method for producing a GaN wafer, comprising: producing a GaNcrystal by the method for producing a GaN crystal according to any oneof (51) to (58) above; and subsequently processing the produced GaNcrystal to form at least one GaN wafer.

The present inventors tried SAG (Selective Area Growth) of GaN on apolar or non-polar GaN surface using GaCl₃ and NH₃ as raw materials andthereby found out that the SAG is feasible and that a GaN island havinga particular shape is formed in the initial stage of the SAG. Anotheraspect of the present invention has been made based on such findings.

The embodiments of the present invention further include the following.

(60) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN seed crystal having a polarsurface whose normal direction forms an angle of not less than 1750 andnot more than 1800 with a [0001] direction of the GaN seed crystal; and(ii) a growth step of growing a GaN crystal comprising a hexagonal prismportion with {10-10} facets as side surfaces, from vapor phase on asurface comprising the polar surface of the GaN seed crystal using GaCl₃and NH₃ as raw materials.

(61) The method for producing a GaN crystal according to (60) above,wherein the hexagonal prism portion terminates with a (000-1) facet.

(62) The method for producing a GaN crystal according to (61) above,wherein the hexagonal prism portion has a {10-1-1} facet as a chamferbetween the (000-1) facet and each of the {10-10} facets.

(63) The method for producing a GaN crystal according to any one of (60)to (62) above, wherein the GaN seed crystal is at least part of a GaNsubstrate, and the polar surface is a main surface of the GaN substrate.

(64) The method for producing a GaN crystal according to (63) above,wherein the GaN substrate is a GaN single crystal substrate.

(65) The method for producing a GaN crystal according to (63) above,wherein the GaN substrate is a template substrate having a basesubstrate and a GaN single crystal layer grown on the base substrate.

(66) The method for producing a GaN crystal according to (63) above,wherein the GaN substrate is a GaN layer-bonded substrate having a basesubstrate and a GaN single crystal layer bonded to the base substrate.

(67) The method for producing a GaN crystal according to any one of (63)to (66) above, wherein in the growth step, a bulk GaN crystal having amaximum growth height of 300 μm or more on the polar surface is grown.

(68) The method for producing a GaN crystal according to (67) above,wherein the maximum growth height of the bulk GaN crystal is 300 μm ormore and less than 500 μm, 500 μm or more and less than 1 mm, 1 mm ormore and less than 3 mm, 3 mm or more and less than 5 mm, 5 mm or moreand less than 10 mm, 10 mm or more and less than 25 mm, 25 mm or moreand less than 50 mm, 50 mm or more and less than 75 mm, 75 mm or moreand less than 100 mm, or 100 mm or more and less than 200 mm.

(69) A method for producing a GaN crystal, comprising a growth step ofgrowing a GaN crystal comprising a hexagonal prism portion with {10-10}facets as side surfaces and having a growth end on a [000-1] side, fromvapor phase using GaCl₃ and NH₃ as raw materials.

(70) The method for producing a GaN crystal according to (69) above,wherein the hexagonal prism portion terminates with a (000-1) facet.

(71) The method for producing a GaN crystal according to (70) above,wherein the hexagonal prism portion has a {10-1-1} facet as a chamferbetween the (000-1) facet and each of the {10-10} facets.

(72) The method for producing a GaN crystal according to any one of (69)to (71) above, wherein in the growth step, the GaN crystal is grown on athree-dimensionally shaped GaN seed crystal.

(73) The method for producing a GaN crystal according to (72) above,wherein the three-dimensionally shaped GaN seed crystal has a hexagonalpyramid portion with {10-1-1} facets as side surfaces.

(74) The method for producing a GaN crystal according to (73) above,wherein the three-dimensionally shaped GaN seed crystal has a hexagonalprism portion arranged on a [0001]side of the hexagonal pyramid portionand having {10-10} facets as side surfaces.

(75) The method for producing a GaN crystal according to (72) above,wherein the three-dimensionally shaped GaN seed crystal has a hexagonalprism portion with {10-10} facets as side surfaces, and the hexagonalprism portion has a [000-1] side terminating with a (000-1) facet.

(76) The method for producing a GaN crystal according to (75) above,wherein the three-dimensionally shaped GaN seed crystal has a hexagonalprism portion with {10-10} facets as side surfaces and a truncatedhexagonal pyramid portion arranged on the [000-1] side of the hexagonalprism portion and having a (000-1) facet as a top surface and {10-1-1}facets as side surfaces.

(77) The method for producing a GaN crystal according to (72) above,wherein the three-dimensionally shaped GaN seed crystal is shaped like atruncated hexagonal pyramid with a (000-1) facet as a top surface, a(0001) facet as a bottom surface, and {10-1-1} facets as side surfaces.

(78) The method for producing a GaN crystal according to any one of (72)to (77) above, wherein in the GaN seed crystal, a ratio of a size in adirection of a c-axis to a size in an arbitrary direction perpendicularto the c-axis is not less than 0.1 and not more than 10.

(79) The method for producing a GaN crystal according to (60) to (78)above, wherein in the growth step, growth of the GaN crystal is repeatedintermittently.

(80) The method for producing a GaN crystal according to any one of (60)to (79) above, wherein the GaCl₃ is generated by reacting metal Ga andCl₂ with each other to produce GaCl and reacting the produced GaCl withCl₂.

(81) The method for producing a GaN crystal according to any one of (60)to (80) above, wherein in the growth step, a GaN is grown at a growthtemperature of 1200° C. or more.

(82) A method for producing a GaN wafer, including: a crystal productionstep of producing a GaN crystal by the method for producing a GaNcrystal according to any one of (60) to (81) above; and a crystalprocessing step of processing the GaN crystal produced in the crystalproduction step to form at least one GaN wafer.

(83) The method for producing a GaN wafer according to (82) above,wherein the GaN wafer formed in the crystal processing step includes aGaN wafer selected from a {10-10} wafer, a {30-3-1} wafer, a {20-2-1}wafer, a {30-3-2} wafer, a {10-1-1} wafer, a {30-31} wafer, a {20-21}wafer, a {30-32} wafer, a {10-11} wafer, a (0001) wafer, and a (000-1)wafer.

Further, still another aspect of the present invention relates to when aGaN substrate surface has a particular semi-polar surface, and theembodiments of the present invention further include the following.

(84) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN seed crystal having asemi-polar surface, a low-index orientation of the GaN seed crystalparallel or nearest parallel to a normal direction of the semi-polarsurface being <10-1-1>; and (ii) a growth step of growing GaN from vaporphase on a surface including the semi-polar surface of the GaN seedcrystal using GaCl₃ and NH₃ as raw materials.

(85) The method for producing a GaN crystal according to (84) above,wherein the normal direction of the semi-polar surface forms an angle of50 or less with <10-1-1> of the GaN seed crystal.

(86) The method for producing a GaN crystal according to (84) above,wherein the semi-polar surface is a {10-1-1} surface.

(87) The method for producing a GaN crystal according to any one of (84)to (86) above, wherein the GaN seed crystal is a GaN {10-1-1} wafer.

(88) The method for producing a GaN crystal according to any one of (84)to (87) above, wherein in the growth step, GaN is grown on thesemi-polar surface at a growth rate of 1 μm/h or more.

(89) The method for producing a GaN crystal according to any one of (84)to (88) above, wherein in the growth step, GaCl₃ is supplied to the GaNseed crystal at a partial pressure of 1.5×10⁻³ atm or more.

(90) The method for producing a GaN crystal according to any one of (84)to (89) above, wherein in the growth step, a product of partialpressures of GaCl₃ and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵atm² or more.

(91) The method for producing a GaN crystal according to any one of (84)to (87) above, wherein in the growth step, a GaN crystal comprising aportion where an FWHM of a (101) plane X-ray rocking curve is less than50 arcsec is formed on the semi-polar surface.

(92) The method for producing a GaN crystal according to any one of (84)to (87) above, wherein in the growth step, a GaN crystal comprising aportion where an FWHM of a (202) plane X-ray rocking curve is less than30 arcsec is formed on the semi-polar surface.

(93) The method for producing a GaN crystal according to (92) above,wherein in the growth step, a GaN crystal comprising a portion where anFWHM of a (202) plane X-ray rocking curve is less than 20 arcsec isformed on the semi-polar surface.

(94) The method for producing a GaN crystal according to (91) above,wherein in the growth step, GaN is grown on the semi-polar surface at agrowth rate of 50 μm/h or more.

(95) The method for producing a GaN crystal according to (94) above,wherein in the growth step, GaN is grown on the semi-polar surface at agrowth rate of 100 μm/h or more.

(96) The method for producing a GaN crystal according to (92) or (93)above, wherein in the growth step, GaN is grown on the semi-polarsurface at a growth rate of 200 μm/h or more.

(97) The method for producing a GaN crystal according to (87) above,wherein in the growth step, a bulk GaN crystal having a maximum growthheight of 300 μm or more on the semi-polar surface is grown.

(98) The method for producing a GaN crystal according to (97) above,wherein the maximum growth height of the bulk GaN crystal is 300 μm ormore and less than 500 μm, 500 μm or more and less than 1 mm, 1 mm ormore and less than 3 mm, 3 mm or more and less than 5 mm, 5 mm or moreand less than 10 mm, 10 mm or more and less than 25 mm, 25 mm or moreand less than 50 mm, 50 mm or more and less than 75 mm, 75 mm or moreand less than 100 mm, or 100 mm or more and less than 200 mm.

(99) A method for producing a GaN crystal, comprising: (i) a seedcrystal preparation step of preparing a GaN seed crystal having a{10-1-1} facet; and (ii) a growth step of growing GaN from vapor phaseon a surface comprising the {10-1-1} facet of the GaN seed crystal usingGaCl₃ and NH₃ as raw materials.

(100) The method for producing a GaN crystal according to (99) above,wherein in the GaN seed crystal, a ratio of a size in a direction of ac-axis to a size in an arbitrary direction perpendicular to the c-axisis not less than 0.1 and not more than 10.

(101) The method for producing a GaN crystal according to (99) or (100)above, wherein the {10-1-1} facet is an as-grown surface.

(102) The method for producing a GaN crystal according to any one of(99) to (101) above, wherein the GaN seed crystal further has a (000-1)facet.

(103) The method for producing a GaN crystal according to (102) above,wherein in the growth step, GaN is also grown on the (000-1) facet.

(104) The method for producing a GaN crystal according to any one of(99) to (103) above, wherein the GaN seed crystal has no {10-10} facet.

(105) The method for producing a GaN crystal according to any one of(99) to (104) above, wherein in the growth step, GaN is grown on the{10-1-1} facet at a growth rate of 1 μm/h or more.

(106) The method for producing a GaN crystal according to any one of(99) to (105) above, wherein in the growth step, GaCl₃ is supplied tothe GaN seed crystal at a partial pressure of 1.5×10⁻³ atm or more.

(107) The method for producing a GaN crystal according to any one of(99) to (106) above, wherein in the growth step, a product of partialpressures of GaCl₃ and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵atm² or more.

(108) The method for producing a GaN crystal according to any one of(99) to (107) above, wherein in the growth step, a GaN crystalcomprising a portion where an FWHM of a (202) plane X-ray rocking curveis less than 30 arcsec is formed on the {10-1-1} facet.

(109) The method for producing a GaN crystal according to (108) above,wherein in the growth step, a GaN crystal comprising a portion where anFWHM of a (202) plane X-ray rocking curve is less than 20 arcsec isformed on the {10-1-1} facet.

(110) The method for producing a GaN crystal according to any one of(84) to (109) above, wherein in the growth step, growth of GaN isrepeated intermittently.

(111) The method for producing a GaN crystal according to any one of(84) to (110) above, wherein in the growth step, the GaCl₃ is generatedby reacting metal Ga and Cl₂ with each other to produce GaCl andreacting the produced GaCl with Cl₂.

(112) The method for producing a GaN crystal according to any one of(84) to (111) above, wherein in the growth step, GaN is grown at agrowth temperature of 1200° C. or more.

(113) A method for producing a GaN wafer, including: a crystalproduction step of producing a GaN crystal by the method for producing aGaN crystal according to any one of (84) to (112) above; and a crystalprocessing step of processing the GaN crystal produced in the crystalproduction step to form at least one GaN wafer.

(114) The method for producing a GaN wafer according to (113) above,wherein the GaN wafer formed in the crystal processing step includes aGaN wafer selected from a {10-10} wafer, a {30-3-1} wafer, a {20-2-1}wafer, a {30-3-2} wafer, a {10-1-1} wafer, a {30-31} wafer, a {20-21}wafer, a {30-32} wafer, a {10-11} wafer, a (0001) wafer, and a (000-1)wafer.

Still further, the embodiments of the present invention further includethe following.

(115) A method for producing a GaN crystal, including: (i) a GaN seedcrystal preparation step of preparing a GaN seed crystal having a mainsurface whose normal direction forms an angle of not less than 850 andnot more than 1800 with a [0001] direction of the GaN seed crystal and apattern mask arranged on the main surface; and (ii) a SAG (SelectiveArea Growth) step of growing GaN from vapor phase on the main surface ofthe GaN seed crystal through the pattern mask using GaCl₃ and NH₃ as rawmaterials.

(116) The production method according to (115) above, wherein thepattern mask comprises an amorphous inorganic thin film.

(117) The production method according to (116) above, wherein theamorphous inorganic thin film comprises a silicon compound.

(118) The production method according to (117) above, wherein theamorphous inorganic thin film comprises SiN_(x).

(119) The production method according to any one of (115) to (118)above, wherein the pattern mask has a dot-shaped opening, and in the SAGstep, a GaN island is formed over the dot-shaped opening.

(120) The production method according to (119) above, wherein thepattern mask has a plurality of dot-shaped openings comprising a firstdot-shaped opening and a second dot-shaped opening, and in the SAG step,a GaN island is formed over each of the first dot-shaped opening and thesecond dot-shaped opening.

(121) The production method according to (120) above, wherein in the SAGstep, the GaN island formed over the first dot-shaped opening and theGaN island formed over the second dot-shaped opening are further allowedto coalesce with each other.

(122) The production method according to any one of (115) to (121)above, wherein in the SAG step, growth of GaN is continued until a GaNlayer covering the main surface is formed.

(123) The production method according to any one of (115) to (122)above, wherein in the SAG step, GaCl₃ is supplied to the GaN seedcrystal at a partial pressure of 1.5×10⁻³ atm or more.

(124) The production method according to any one of (115) to (122)above, wherein in the SAG step, a product of partial pressures of GaCl₃and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵ atm² or more.

(125) The production method according to any one of (115) to (124)above, wherein the GaN seed crystal is at least part of a GaN substrate.

(126) The production method according to (125) above, wherein the GaNsubstrate is a GaN single crystal substrate.

(127) The production method according to any one of (115) to (126)above, wherein a normal direction of the main surface forms an angle of1750 or more with a [0001] direction of the GaN seed crystal.

(128) A method for producing a GaN crystal, comprising: (i) a GaN seedcrystal preparation step of preparing a GaN seed crystal having a polarsurface whose normal direction forms an angle of not less than 1750 andnot more than 1800 with a [0001] direction of the GaN seed crystal and apattern mask arranged on the polar surface and provided with adot-shaped opening; and (ii) a SAG (Selective Area Growth) step ofgrowing GaN from vapor phase on the polar surface of the GaN seedcrystal through the pattern mask using GaCl₃ and NH₃ as raw materials,the SAG step including forming a GaN island comprising a hexagonal prismportion over the dot-shaped opening.

(129) The production method according to (128) above, wherein thehexagonal prism portion has {10-10} facets as side surfaces.

(130) The production method according to (129) above, wherein thehexagonal prism portion terminates with a (000-1) facet.

(131) The production method according to (130) above, wherein thehexagonal prism portion has a {10-1-1} facet as a chamfer between the(000-1) facet and each of the {10-10} facets.

(132) The production method according to any one of (128) to (131)above, wherein the GaN seed crystal is at least part of a GaN substrate.

(133) The production method according to (132) above, wherein the GaNseed crystal is a GaN single crystal substrate.

(134) The production method according to (133) above, wherein the GaNsingle crystal substrate is an off-cut (000-1) wafer.

(135) The production method according to any one of (128) to (134)above, wherein the pattern mask comprises an amorphous inorganic thinfilm.

(136) The production method according to (135) above, wherein theamorphous inorganic thin film comprises a silicon compound.

(137) The production method according to (136) above, wherein theamorphous inorganic thin film comprises SiN_(x).

(138) The production method according to any one of (128) to (137)above, wherein in the SAG step, GaCl₃ is supplied to the GaN seedcrystal at a partial pressure of 1.5×10⁻³ atm or more.

(139) The production method according to any one of (128) to (138)above, wherein in the SAG step, a product of partial pressures of GaCl₃and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵ atm² or more.

Effect of the Invention

According to one embodiment of the present invention, a novel method forproducing a GaN crystal is provided, the method comprising growing GaNfrom vapor phase on a semi-polar or non-polar GaN surface using GaCl₃and NH₃ as raw materials.

According to another embodiment of the present invention, a novel methodfor producing a GaN crystal is provided, the method comprising growing aGaN crystal having a particular shape from vapor phase using GaCl₃ andNH₃ as raw materials.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a flow chart of a GaN crystal production method accordingto the embodiments.

FIG. 2 is a perspective view illustrating one example of a GaN substratewhich is usable in the GaN crystal production method according to theembodiments.

FIG. 3 illustrates a GaN single crystal having a first main surface as asurface when viewed from a direction parallel to an intersection linebetween the C-plane of the GaN single crystal and the first mainsurface.

FIG. 4 is a perspective view illustrating an example of the shape of aGaN seed crystal.

FIG. 5 is a perspective view illustrating an example of the shape of aGaN seed crystal.

FIG. 6 is a perspective view illustrating an example of the shape of aGaN seed crystal.

FIG. 7 is a perspective view illustrating an example of the shape of aGaN seed crystal.

FIG. 8 is a perspective view illustrating an example of the shape of aGaN seed crystal.

FIG. 9A is a perspective view illustrating an example of the shape of aGaN seed crystal.

FIG. 9B is a cross-sectional view illustrating an example of the shapeof a GaN seed crystal.

FIG. 10 is a schematic diagram of a crystal growth apparatus usable inthe GaN crystal production method according to the embodiments.

FIG. 11 is a schematic diagram of a crystal growth apparatus usable inthe GaN crystal production method according to the embodiments.

FIG. 12 is a graph showing the relationship between the growth rate ofGaN and the product of a GaCl₃ partial pressure and an NH₃ partialpressure in a growth zone.

FIG. 13A is a planar image illustrating SEM image (photographs) of a GaNisland formed by SAG on a GaN substrate.

FIG. 13B is a bird's-eye image illustrating SEM image (photograph) of aGaN island formed by SAG on a GaN substrate.

FIG. 14A is a planar image illustrating SEM image (photograph) of a GaNisland formed by SAG on a GaN substrate.

FIG. 14B is a bird's-eye image illustrating SEM image (photograph) of aGaN island formed by SAG on a GaN substrate.

FIG. 15A is a planar image illustrating SEM image (photographs) of a GaNisland formed by SAG on a GaN substrate.

FIG. 15B is a bird's-eye image illustrating SEM image (photograph) of aGaN island formed by SAG on a GaN substrate.

FIG. 16A is a planar image illustrating SEM image (photograph) of a GaNisland formed by SAG on a GaN substrate.

FIG. 16B is a bird's-eye image illustrating SEM image (photograph) of aGaN island formed by SAG on a GaN substrate.

FIG. 17A is a bird's-eye SEM image of a GaN island formed by SAG on aGaN (000-1) substrate (photograph).

FIG. 17B is bird's-eye SEM image of a GaN island formed by SAG on a GaN(10-10) substrate (photograph).

FIG. 18A is a bird's-eye SEM image of a GaN island formed by SAG on aGaN (000-1) substrate (photograph).

FIG. 18B is bird's-eye SEM image of a GaN island formed by SAG on a GaN(10-10) substrate (photograph).

DESCRIPTION OF EMBODIMENTS

GaN has a wurtzite-type crystal structure belonging to a hexagonalsystem. In GaN, a crystal axis parallel to [0001] and [000-1] isreferred to as a c-axis, a crystal axis parallel to <10-10> is referredto an m-axis, and a crystal axis parallel to <11-20> is referred to ana-axis. A crystal plane perpendicular to the c-axis is referred to as aC-plane, a crystal plane perpendicular to the m-axis is referred to as aM-plane, and a crystal plane perpendicular to the a-axis is referred toas an A-plane.

GaN surfaces perpendicular to the c-axis include a (0001) surface(gallium polar surface) and a (000-1) surface (nitrogen polar surface).Such surfaces are also referred to as polar surfaces.

A GaN surface parallel to the c-axis, that is, a GaN surface for which 1of Miller indices {hkil} is 0 (zero) such as a {10-10} surface and a{11-20} surface, is referred to as a non-polar surface.

A GaN crystal surface which is neither a polar surface nor a non-polarsurface is referred to as a semi-polar surface.

In the present specification, unless otherwise noted, reference made toa crystal axis, a crystal surface, a crystal orientation, and the likemeans a crystal axis, a crystal surface, a crystal orientation, and thelike of GaN.

1. Method for Producing GaN Crystal

As shown in a flow chart in FIG. 1, the GaN crystal production methodaccording to the embodiments comprises the following two steps.

(S1) A seed crystal preparation step of preparing a GaN seed crystalcomprising a non-polar or semi-polar surface whose normal directionforms an angle of 850 or more and less than 1700 with the [0001]direction of the GaN seed crystal.

(S2) A growth step of growing GaN from vapor phase using GaCl₃ and NH₃as raw materials on a surface including the non-polar or semi-polarsurface of the GaN seed crystal prepared in the seed crystal preparationstep.

The GaN seed crystal prepared in the above-described seed crystalpreparation step (S1) may have two or more non-polar or semi-polarsurfaces, in which case, it is only necessary to satisfy a conditionthat at least one of the two or more non-polar or semi-polar surfaceshas a normal direction forming an angle of 850 or more and less than1700 with the [0001] direction of the GaN seed crystal.

The GaN crystal production method according to the embodiments mayfurther comprise another step in addition to the seed crystalpreparation step and the growth step described above.

Hereinafter, more detailed description will be given with reference todrawings.

1.1. GaN Seed Crystal [1] GaN Substrate

The GaN crystal production method according to the embodiments uses aGaN seed crystal. The GaN seed crystal may be a GaN substrate or a partof a GaN substrate.

FIG. 2 is a perspective view illustrating one example of a GaN substratewhich is usable as the seed crystal in the GaN crystal production methodaccording to the embodiments. Referring to FIG. 2, a GaN substrate 10has a first main surface 11 which is a main surface on one side and asecond main surface 12 which is a main surface on the opposite side. Thefirst main surface and the second main surface are connected to eachother via a side surface 13.

Although the first main surface 11 and the second main surface 12 of theGaN substrate 10 are rectangular, they are not limited thereto and maybe circular, hexagonal, or in any other shape. Usually, the first mainsurface 11 and the second main surface 12 are parallel to each other.

The first main surface 11 usually has an area of 1 cm² or more,preferably 2 cm² or more, more preferably 4 cm² or more, more preferably10 cm² or more. The first main surface 11 may have an area of 10 cm² ormore and less than 40 cm², 40 cm² or more and less than 60 cm², 60 cm²or more and less than 120 cm², 120 cm² or more and less than 180 cm², or180 cm² or more.

The GaN substrate 10 usually has a thickness t of 200 μm or more,preferably 250 μm or more, more preferably 300 μm or more or may be madethicker depending on the area of the first main surface 11.

At least a portion including the first main surface 11 in the GaNsubstrate 10 is formed of a GaN single crystal. In other words, thefirst main surface 11 is a surface of a GaN single crystal.

FIG. 3 illustrates a GaN single crystal 1 which makes up a portionincluding the first main surface 11 in the GaN substrate 10 when viewedfrom a direction parallel to the intersection line between the C-planeof the GaN single crystal 1 and the first main surface. The first mainsurface 11 is a surface of the GaN single crystal 1. In FIG. 3, theintersection line between the C-plane of the GaN single crystal 1 andthe first main surface 11 is perpendicular to the plane of paper.

The first main surface 11 has a normal direction Dn forming an angle θwith the [0001] direction of the GaN single crystal 1. The angle θ is85° or more and less than 170°. The angle θ may be, for example, 85° ormore and less than 90°, 90° or more and less than 93°, 93° or more andless than 97°, 97° or more and less than 102°, 102° or more and lessthan 107°, 107° or more and less than 112°, 112° or more and less than122°, or 122° or more and less than 132°.

In a preferred example, the angle θ formed by the normal direction Dn ofthe first main surface 11 with the [0001] direction of the GaN singlecrystal 1 is 87° or less or 930 or more. This is because if the angle θis within a range of 90°±approximately 20, when GaN is epitaxially grownon the first main surface during the growth step which will be describedlater, a GaN crystal having a relatively low quality tends to be formed.

The normal direction Dn of the first main surface 11 and the [0001]direction of the GaN single crystal 1 are in such a relationship thatthe former overlaps the latter when the former is rotated around theintersection line between the C-plane of the GaN single crystal 1 andthe first main surface 11 as a rotation axis.

The direction of the intersection line is not limited, but is preferablyin the a-axis direction ±15°, more preferably in the a-axis direction±5°, more preferably in the a-axis direction ±30, more preferably in thea-axis direction ±20, more preferably in the a-axis direction ±1°.

In a preferred example, the low-index orientation of the GaN singlecrystal 1 parallel or nearest parallel to the normal direction of thefirst main surface 11 may be <10-10>, <30-3-1>, <20-2-1>, <30-3-2> or<10-1-1>. Herein, a crystal orientation for which all of the absolutevalues of integers h, k, i, and l of Miller indices <hkil> are smallerthan or equal to 3 is referred to as a low-index orientation.

When the first main surface 11 has a normal direction parallel to<10-10> of the GaN single crystal 1, an angle formed between the normaldirection and the [0001] direction of the GaN single crystal 1 is 90°,and the intersection line between the first main surface 11 and theC-plane of the GaN single crystal 1 extends in the a-axis direction.

When the first main surface 11 has a normal direction parallel to<30-3-1> of the GaN single crystal 1, an angle formed between the normaldirection and the [0001] direction of the GaN single crystal 1 is100.10, and the intersection line between the first main surface 11 andthe C-plane of the GaN single crystal 1 extends in the a-axis direction.

When the first main surface 11 has a normal direction parallel to<20-2-1> of the GaN single crystal 1, an angle formed between the normaldirection and the [0001] direction of the GaN single crystal 1 is104.9°, and the intersection line between the first main surface 11 andthe C-plane of the GaN single crystal 1 extends in the a-axis direction.

When the first main surface 11 has a normal direction parallel to<30-3-2> of the GaN single crystal 1, an angle formed between the normaldirection and the [0001] direction of the GaN single crystal 1 is109.5°, and the intersection line between the first main surface 11 andthe C-plane of the GaN single crystal 1 extends in the a-axis direction.

When the first main surface 11 has a normal direction parallel to<10-1-1> of the GaN single crystal 1, an angle formed between the normaldirection and the [0001] direction of the GaN single crystal 1 is 118°,and the intersection line between the first main surface 11 and theC-plane of the GaN single crystal 1 extends in the a-axis direction.

When the first main surface 11 has a normal direction parallel to<20-2-3> of the GaN single crystal 1, an angle formed between the normaldirection and the [0001] direction of the GaN single crystal 1 is128.6°, and the intersection line between the first main surface 11 andthe C-plane of the GaN single crystal 1 extends in the a-axis direction.

Preferably, the GaN substrate 10 is a GaN single crystal substrate.

It is known that bulk GaN single crystals grown by various methodsincluding an HVPE method, a flux method, and a sublimation method can besliced in an arbitrary direction to thereby fabricate GaN single crystalsubstrates having various surface orientations. For example,WO2008/059875 discloses a large area non-polar or semi-polar GaN singlecrystal substrate which is cut out from a bulk GaN crystal grown on aplurality of rectangular substrates disposed adjoining each other.

The GaN substrate 10 may be a template substrate comprising a basesubstrate and a GaN single crystal layer epitaxially grown on the basesubstrate. In this case, the surface of the GaN single crystal layercorresponds to the first main surface 11.

Typically, the base substrate is a single crystal substrate (heterosubstrate) made of a material differing in composition from GaN, such asa sapphire substrate, a spinel substrate, an AlN substrate, a SiCsubstrate, and a Si substrate. The epitaxial growth method may be avapor phase growth method such as an MOVPE method and an HVPE method ormay be a flux method.

The GaN substrate 10 may be a GaN layer-bonded substrate comprising abase substrate and a GaN single crystal layer bonded to the basesubstrate. In this case, the surface of the GaN single crystal layercorresponds to the first main surface 11.

GaN layer-bonded substrates are formed by a method comprising: bonding abulk GaN single crystal to the base substrate; and subsequently cuttingthe bulk GaN single crystal such that a GaN single crystal layer is lefton the base substrate side. The base substrate may be any of varioussingle crystal substrates or may be a metal substrate, a ceramicsubstrate, a polycrystalline GaN substrate, or the like.

Preferably, the first main surface 11 of the GaN substrate 10 is asurface which has been planarized by mechanical polishing (such asgrinding and lapping) and subsequently been subjected to finishingprocess including dry etching and/or CMP (Chemical Mechanical Polishing)so that crystal defects introduced by the mechanical polishing areremoved.

In one example, the first main surface 11 of the GaN substrate 10 may bean as-grown GaN surface.

In one example, on the first main surface 11 of the GaN substrate 10, apattern mask for causing SAG (Selective Area Growth) may be arranged.The material for the pattern mask is for example SiN_(x). On a SiN_(x)thin film, vapor phase growth of GaN from GaCl₃ and NH₃ is inhibited.Amorphous inorganic thin films made of other materials, for example asilicon oxide film or a silicon oxynitride film are also usable as amaterial for the pattern mask.

The pattern mask may be provided with an opening shaped like a dot, suchas a circle or a regular polygon. The dot-shaped openings may bearranged for example in a closest packed manner. In the closest packedarrangement, each opening is arranged at a lattice position of a regulartriangle lattice (a vertex of a regular triangle).

The pattern mask may be provided with a linear opening. Thus, thepattern mask may be a stripe mask.

[2] Three-Dimensionally Shaped GaN Seed Crystal

The GaN seed crystal used in the GaN crystal production method accordingto the embodiments may be a GaN crystal having a three-dimensionalshape. Preferably, in the three-dimensionally shaped GaN seed crystal,the ratio of its size in the c-axis direction and its size in anarbitrary direction perpendicular to the c-axis is 0.1 or more and 10 orless. The ratio may be 0.2 or more, further may be 0.3 or more, and maybe 5 or less, further may be 3 or less.

Examples of the shapes of the three-dimensionally shaped GaN seedcrystals that are usable in the GaN crystal production method accordingto the embodiments are illustrated in FIGS. 4 to 9.

FIG. 4 illustrates a GaN seed crystal which has a hexagonal prismportion with {10-10} facets as side surfaces, a first hexagonal pyramidportion with {10-1-1} facets as side surfaces, and a second hexagonalpyramid portion with {10-11} facets as side surfaces. The firsthexagonal pyramid portions are arranged on the [000-1] side of thehexagonal prism portion, while the second hexagonal pyramid portions areon the [0001] side.

The GaN seed crystal illustrated in FIG. 4 can be produced by a liquidphase growth method such as a Na flux method and an ammonothermalmethod.

FIG. 5 illustrates a GaN seed crystal which has a hexagonal prismportion with {10-10} facets as side surfaces and a hexagonal pyramidportion with {10-1-1} facets as side surfaces arranged on the [000-1]side of the hexagonal prism portion. The [0001] side of the hexagonalprism portion terminates with a (0001) facet.

The GaN seed crystal illustrated in FIG. 5 can be produced for exampleby removing, through cutting or polishing, the second hexagonal pyramidportion from the GaN seed crystal illustrated in FIG. 4.

FIG. 6 illustrates a GaN seed crystal which has a hexagonal prismportion with {10-10} facets as side surfaces and a hexagonal pyramidportion with {10-11} facets as side surfaces arranged on the [0001] sideof the hexagonal prism portion. The [000-1] side of the hexagonal prismportion terminates with a (000-1) facet.

The GaN seed crystal illustrated in FIG. 6 can be produced for exampleby removing, through cutting or polishing, the first hexagonal pyramidportion from the GaN seed crystal illustrated in FIG. 4.

FIG. 7 is a perspective view illustrating yet another example of the GaNseed crystal prepared in the seed crystal preparation step.

FIG. 7 illustrates a GaN seed crystal which has a hexagonal prismportion with {10-10} facets as side surfaces and a truncated hexagonalpyramid portion with a (000-1) facet as a top surface and {10-1-1}facets as side surfaces arranged on the [000-1] side of the hexagonalprism portion. The [0001] side of the hexagonal prism portion terminateswith a (0001) facet.

The GaN seed crystal illustrated in FIG. 7 can be produced for exampleby a crystal growth method disclosed in JP-A-2013-212978.

FIG. 8 illustrates a GaN seed crystal which is shaped like a truncatedhexagonal pyramid with a (000-1) facet as a top surface, a (0001) facetas a bottom surface, and {10-1-1} facets as side surfaces.

The GaN seed crystal illustrated in FIG. 8 can be produced for exampleby a crystal growth method disclosed in JP-A-2013-212978.

FIGS. 9A and 9B illustrate a GaN seed crystal which can be produced by acrystal growth method disclosed in JP-A-2013-212978, and FIG. 9A is aperspective view while FIG. 9B is a cross-sectional view when cut alonga plane perpendicular to the longitudinal direction of the crystal.

In the GaN seed crystals illustrated by examples in FIGS. 4 to 9B,{10-10} facets and {10-1-1} facets can be as-grown surfaces.Alternatively, these facets may be etched surfaces.

1.2. Vapor Phase Growth Apparatus

In the GaN crystal production method according to the embodiments, avapor phase growth apparatus provided with a first zone, a second zone,and a growth zone can be preferably used for growing GaN from GaCl₃ andNH₃. In the first zone, Cl₂ and metal Ga react with each other togenerate GaCl. In the second zone, GaCl generated in the first zonereacts with Cl₂ to generate GaCl₃. In the growth zone, NH₃ and gaseousgallium chloride including GaCl₃ react with each other to generate GaNwhich epitaxially grows on a GaN seed crystal.

One example of the above-described vapor phase growth apparatus havingthe first zone, the second zone, and the growth zone is schematicallyillustrated in FIG. 10.

Referring to FIG. 10, a vapor phase growth apparatus 100 has a firstreaction tube 110 and a second reaction tube 120. A first zone Z1 and asecond zone Z2 are provided in the first reaction tube 110, and a growthzone Z3 is provided in the second reaction tube 120.

The first reaction tube 110 and the second reaction tube 120 may beformed of, without limitation, quartz.

In the first zone Z1 in the first reaction tube 110, metal Ga is placed.A container for metal Ga is for example a quartz boat.

The first reaction tube 110 has a first Cl₂ supply port 111 providedupstream of the first zone Z1 and a second Cl₂ supply port 112 provideddownstream of the first zone Z1. The second zone Z2 starts from theposition of the second Cl₂ supply port 112 and extends downstream.

An external heater (not illustrated) is arranged outside the firstreaction tube 110 such that the first zone Z1 and the second zone Z2 canbe heated by the external heater independently from each other. Examplesof the external heater include resistance heaters, induction heaters,and lamp heaters.

In the first zone Z1, Cl₂ introduced through the first Cl₂ supply port111 reacts with metal Ga to generate gaseous gallium chloride. The maincomponent of the gaseous gallium chloride is GaCl generated by thefollowing reaction.Ga(l)+½Cl₂(g)→GaCl(g)In the reaction formula above, each of (l), (s) and (g) denotes that thesubstance is a respective one of a liquid, a solid, and a gas (the sameapplies hereinafter).

In the second zone Z2, Cl₂ introduced through the second Cl₂ supply port112 reacts with gaseous gallium chloride transported from the first zoneZ1. The main reaction is a GaCl₃ generation reaction, which is asfollows.GaCl(g)+Cl₂(g)→GaCl₃(g)

The first reaction tube 110 has a gas outlet 113 at a downstream endthereof. The first reaction tube 110 has a downstream portion which isinserted into the second reaction tube 120, and gallium chloridegenerated in the first reaction tube is transported through the gasoutlet 113 into the second reaction tube 120.

The second reaction tube 120 has a NH₃ supply port 121 provided upstreamof the growth zone Z3 and an exhaust port 122 provided downstream of thegrowth zone Z3. The gas outlet 113 of the first reaction tube 110 ispositioned upstream of the growth zone Z3.

In the growth zone Z3, a susceptor 130 to put a GaN seed crystal on isplaced. The susceptor 130 is formed of carbon, for example.

An external heater (not illustrated) for heating a GaN seed crystalplaced on the susceptor 130 such that the GaN seed crystal is heatedtogether with the susceptor is arranged outside the second reaction tube120. Examples of the external heater include resistance heaters,induction heaters, and lamp heaters. In one example, instead of or inaddition to the external heater, a resistance heater may be providedinside the susceptor 130.

In the growth zone Z3, NH₃ and gaseous gallium chloride including GaCl₃react with each other to generate GaN. The generated GaN epitaxiallygrows on the GaN seed crystal.

The vapor phase growth apparatus used in the growth step may bevariously modified while having the same basic configuration as that ofthe vapor phase growth apparatus illustrated in FIG. 10. One example ofsuch modified vapor phase growth apparatuses is illustrated in FIG. 11.In FIG. 11, elements corresponding to the elements of the vapor phasegrowth apparatus illustrated in FIG. 10 are allotted with the samereference signs as those in FIG. 10.

In contrast with the apparatus in FIG. 10 in which the first reactiontube 110 is an L-shaped tube only whose downstream portion including thegas outlet 113 is inserted into the second reaction tube 120, in theapparatus in FIG. 11, the first reaction tube 110 is a straight tubewhose entirety is placed in the second reaction tube 120.

The above is not the only difference between the apparatus in FIG. 11and the apparatus in FIG. 10.

For example, the vapor phase growth apparatus 100 in FIG. 11 has afunnel-shaped tube 114 provided between the first zone Z1 and the secondzone Z2 in the first reaction tube 110 for decreasing thecross-sectional area of the flow path gradually from the upstream sideto the downstream side, with a view to increasing the flow pathresistance on the downstream side to thereby increase Cl₂ partialpressure in the first zone Z1 and enhance the efficiency of GaClgeneration in the zone.

Further, the vapor phase growth apparatus 100 in FIG. 11 has baffles 115provided in the second zone Z2 with a view to improving the efficiencyof GaCl₃ generation. Placement of the baffles causes extension of flowpath length resulting in a longer period of time during which GaCl andCl₂ stay in the second zone, and in addition causes gas flow disturbancewhich are expected to have an enhancing effect on mixing of GaCl andCl₂.

In a preferred example, in each vapor phase growth apparatus 100illustrated in FIGS. 10 and 11, the gas outlet 113 of the first reactiontube 110 may be structured as a double tube and configured to releasegallium chloride gas through an inner tube and a barrier gas through anouter tube. This is to enclose a gallium chloride gas flow exiting fromthe gas outlet 113 within a barrier gas flow so as to prevent galliumchloride from reacting with NH₃ before reaching the growth zone Z3. Usedas the barrier gas is an inert gas, specifically N₂ (nitrogen gas) or anoble gas (such as Ar).

In addition, in the vapor phase growth apparatus 100 of FIG. 10 or 11,the first reaction tube 110 and the second reaction tube 120 may be eachprovided suitably with a gas supply port dedicated for a carrier gas.Used as the carrier gas is an inert gas, specifically N₂ (nitrogen gas)or a noble gas (such as Ar).

In the vapor phase growth apparatus illustrated in FIG. 10, the L-shapedfirst reaction tube 110 may be arranged such that one of the linearportions is vertical and the other is horizontal, or may be arrangedsuch that both of the linear portions are horizontal.

In the vapor phase growth apparatus illustrated in FIG. 11, the firstreaction tube 110 and the second reaction tube 120 may extend either ina vertical direction or in a horizontal direction or may be tilted.

The vapor phase growth apparatus illustrated in FIG. 10 or 11 may besuitably provided with a mechanism for rotating the susceptor 130.

Although examples of the vapor phase growth apparatus preferably usablefor vapor phase growth of GaN using GaCl₃ and NH₃ as raw materials havebeen described above, the vapor phase growth apparatus usable in the GaNcrystal production method according to the embodiments is not limited bythose described above. For instance, it is also possible to use a vaporphase growth apparatus of the type which vaporizes solid GaCl₃ togenerate gaseous GaCl₃ as disclosed in Patent Document 1.

1.3. Vapor Phase Growth of GaN

Using the vapor phase growth apparatus 100 illustrated in FIG. 10 or 11,vapor phase growth of GaN can be achieved on a GaN seed crystal inaccordance with the following procedure.

First, a GaN seed crystal is set on the susceptor 130 arranged in thesecond reaction tube 120.

A quartz boat containing metal gallium is placed in the first zone Z1 inthe first reaction tube 110.

Next, a carrier gas is flown through the first reaction tube 110 and thesecond reaction tube 120 to make the inner atmospheres in these reactiontubes into carrier gas atmospheres. As previously described, an inertgas, specifically N₂ or a noble gas is used as the carrier gas. Abarrier gas may also be allowed to start flowing at this timing.

The carrier gas may be introduced into the reaction tubes through theCl₂ supply ports and/or the NH₃ supply port, and also may be introducedinto the reaction tubes through supply ports dedicated for inert gassesand suitably provided in the reaction tubes.

Further, through the NH₃ supply port 121, supply of NH₃ into the secondreaction tube 120 is started. When necessary, NH₃ is introduced into thesecond reaction tube 120 together with the carrier gas.

After starting supply of NH₃, the GaN seed crystal is heated to apredetermined growth temperature by using the external heater (notillustrated).

The growth temperature is usually 90° C. or higher. As shown in theexperimental results to be described later, even at a growth temperatureof 1200° C. or higher and further at a growth temperature of 1300° C. orhigher, GaN is growable at a growth rate sufficient for practical uses.

While the growth temperature has no particular upper limit, in order toprevent the vapor phase growth apparatus from malfunctioning due to thethermal deterioration of parts including the reaction tubes, the growthtemperature is preferably set to lower than 1500° C. and more preferablylower than 1400° C.

The pressure in the second reaction tube 120 (pressure in the growthzone) is regulated by an external exhauster (such as a fan) connected tothe exhaust port 122 of the second reaction tube such that the pressurehas a constant value, for example, within the range of from 0.8 to 1.2atm.

By using the external heater (not illustrated), the first reaction tubeis heated to reach a predetermined temperature before the GaN seedcrystal reaches the predetermined growth temperature.

Setting the temperature of the first zone Z1 to 400° C. or higher makesit possible that gallium chloride species generated in the zone aremostly GaCl (see FIG. 5 of Patent Document 2).

From the viewpoint of increasing GaCl generation rate, the first zone Z1is at a temperature of preferably 500° C. or more, more preferably 700°C. or more. From the viewpoint of preventing shorter life of the firstreaction tube due to thermal deterioration, the first zone Z1 is at atemperature of preferably 1000° C. or less, more preferably 90° C. orless, more preferably 850° C. or less.

The second zone Z2 is heated at least to a temperature at which GaClsupplied from the first zone Z1 does not precipitate on the wall of thereaction tube.

Setting the temperature of the second zone Z2 to 200° C. or higher makesit possible that gallium chloride species generated in the zone aremostly GaCl₃ (see FIG. 6 of Patent Document 2).

The second zone Z2 may be at a temperature of less than 200° C., sincegallium chloride species generated are mostly GaCl₃ or a dimer ofgallium trichloride represented by (GaCl₃)₂. This dimer will change intoGaCl₃ in the growth zone Z3 which is heated to a high temperature.

From the viewpoint of increasing GaCl₃ generation rate, the second zoneZ2 is at a temperature of preferably 500° C. or more, more preferably700° C. or more. From the viewpoint of preventing shorter life of thefirst reaction tube due to thermal deterioration, the second zone Z2 isat a temperature of preferably 1000° C. or less, more preferably 90° C.or less, more preferably 850° C. or less.

From the viewpoint of stabilizing the gas flow, it is preferable to setthe temperature of the second zone Z2 to be equal to the temperature ofthe first zone Z1.

Once the GaN seed crystal reaches the predetermined growth temperature,Cl₂ is immediately supplied through each of the first Cl₂ supply port111 and the second Cl₂ supply port 112 into the first reaction tube 110to generated gallium chloride. Cl₂ is introduced into the first reactiontube 110 together with the carrier gas as necessary. Used as the carriergas is an inert gas, specifically N₂ or a noble gas.

When the gallium chloride generated in the first reaction tube 110reaches the growth zone in the second reaction tube 120, epitaxialgrowth of GaN starts on the GaN seed crystal.

The flow rate of Cl₂ supplied to the first reaction tube 110 and theflow rate of NH₃ supplied to the second reaction tube 120 are set suchthat the total pressure and the Cl₂ partial pressure in each of thefirst zone Z1 and the second zone Z2 and the total pressure, the GaCl₃partial pressure, and the NH₃ partial pressure in the growth zone Z3,are each within a desired range.

In the first zone Z1, for example, the Cl₂ partial pressure is 1.0×10⁻³atm or higher, and the total pressure is from 0.8 to 1.2 atm.

In the second zone Z2, for example, the Cl₂ partial pressure is 2.0×10⁻³atm or higher, and the total pressure is from 0.8 to 1.2 atm.

In the growth zone Z3, for example, the GaCl₃ partial pressure is from9.0×10⁻³ to 1.0×10⁻¹ atm, the NH₃ partial pressure is from 5.0×10⁻² to2.5×10⁻¹ atm, and the total pressure is from 0.8 to 1.2 atm.

The GaCl₃ partial pressure in the growth zone Z3 is in other words thepartial pressure of GaCl₃ supplied to the GaN seed crystal.

The GaCl₃ partial pressure in the growth zone Z3 may be less than9.0×10⁻³ atm, and may be for example 1.5×10⁻³ atm or more and less than2.4×10⁻³ atm, 2.4×10⁻³ atm or more and less than 4.1×10⁻³ atm, or4.1×10⁻³ atm or more and less than 9.0×10⁻³ atm.

The growth rate of GaN is controllable by the partial pressures of GaCl₃and NH₃ supplied to the GaN seed crystal. For instance, the product ofthe GaCl₃ partial pressure and the NH₃ partial pressure in the growthzone Z3 may be set to 9.5×10⁻⁵ atm² or more and less than 3.2×10⁻⁴ atm²,3.2×10⁻⁴ atm² or more and less than 7.0×10⁻⁴ atm², 7.0×10⁻⁴ atm² or moreand less than 9.8×10⁻⁴ atm², or 9.8×10⁻⁴ atm² or more.

When terminating the growth of GaN, the supply of Cl₂ to the firstreaction tube 110 is stopped to thereby stop the supply of galliumchloride to the growth zone Z3. At the same time, heating of GaN seedcrystal is stopped to allow the reaction tube temperature of the secondreaction tube to drop to room temperature. To prevent the degradation ofgrown GaN, NH₃ and the carrier gas are flown through the second reactiontube 120 also during lowering the temperature.

Among surfaces of a GaN seed crystal, it is a surface whose normaldirection forms an angle of not less than 85° and not more than 180°with the [0001] direction of the GaN seed crystal on which GaN can begrown from GaCl₃ and NH₃. The growth rate of GaN on such a surface maybe 1 μm/h or more.

The growth rate may be set to, for example, 1 μm/h or more and less than5 μm/h, 5 μm/h or more and less than 10 μm/h, 10 μm/h or more and lessthan 15 μm/h, 15 μm/h or more and less than 20 μm/h, 20 μm/h or more andless than 25 μm/h, 25 μm/h or more and less than 50 μm/h, 50 μm/h ormore and less than 75 μm/h, 75 μm/h or more and less than 100 μm/h, 100μm/h or more and less than 125 μm/h, 125 μm/h or more and less than 150μm/h, 150 μm/h or more and less than 175 μm/h, 175 μm/h or more and lessthan 200 μm/h, 200 μm/h or more and less than 250 μm/h, 250 μm/h or moreand less than 300 μm/h, 300 μm/h or more and less than 400 μm/h, 400μm/h or more and less than 500 μm/h, or 500 μm/h or more and less than2000 μm/h.

A growth rate of GaN on a certain GaN surface can be examined by growinga GaN crystal layer on the GaN surface and dividing the thickness of thegrown GaN crystal layer by the growth time.

When using a crystal growth apparatus of the type illustrated in FIG. 10or FIG. 11, the growth time may be a period of time between the start ofCl₂ supply to the first reaction tube and the stop of the Cl₂ supply.When using other types of crystal growth apparatuses, the reaction timemay be a period of time between the start of GaCl₃ supply to a growthchamber and the stop of the supply.

As a general tendency, the lower the growth rate is, the better thecrystallinity of the grown GaN crystal is. Thus, GaN has a growth rateof preferably less than 150 μm/h, more preferably less than 125 μm/h.

An exception is when a GaN crystal is grown on the {10-1-1} surface ofGaN, in which case it is possible that a GaN crystal grown at a rate of200 μm/h or more is of the quality equal to or higher than that of a GaNcrystal grown at a rate of about 100 μm/h.

It is understood form this that the use of a GaN seed crystal which has,like a GaN {10-1-1} wafer, a semi-polar surface whose low indexorientation parallel or nearest parallel to the normal direction is<10-1-1> is particularly advantageous in efficiently producing highquality GaN crystals.

When a GaN substrate is used as a GaN seed crystal, GaN grown on the GaNsubstrate may be a film whose thickness is equal to or less than thethickness of the GaN substrate or may be a bulk crystal whose maximumgrowth height on a main surface of the GaN substrate is greater than thethickness of the GaN substrate.

The growth height herein refers to the height of a bulk GaN crystalgrown on a base GaN surface when the base GaN surface is used as areference plane, in other words, the distance from the base GaN surfaceto the top surface of the bulk GaN crystal. The maximum growth heightrefers to a growth height at a position where the above-defined growthheight is the maximum.

When a bulk GaN crystal is grown on a GaN substrate, the bulk GaNcrystal may have, on a main surface of the GaN substrate, a maximumgrowth height of 300 μm or more and less than 500 μm, 500 μm or more andless than 1 mm, 1 mm or more and less than 3 mm, 3 mm or more and lessthan 5 mm, 5 mm or more and less than 10 mm, 10 mm or more and less than25 mm, 25 mm or more and less than 50 mm, 50 mm or more and less than 75mm, 75 mm or more and less than 100 mm, or 100 mm or more and less than200 mm, for example.

When a GaN seed crystal has two or more surfaces on which GaN can begrown by vapor phase epitaxy using GaCl₃ and NH₃ as raw materials, GaNcan be grown on each of such surfaces at the growth rate describedabove.

For instance, when the GaN seed crystal illustrated in FIG. 4 or 5 isused, GaN is growable on each of the six {10-10} facets and the six{10-1-1} facets at a growth rate of 1 μm/h or more.

For instance, when the GaN seed crystal illustrated in FIG. 7 is used,GaN is growable on each of the six {10-10} facets, the six {10-1-1}facets, and the (000-1) facet at a growth rate of 1 μm/h or more.

The growth of GaN on a GaN seed crystal may be repeated intermittently.In other words, the growth of GaN may be separated into and carried outin a plurality of growth batches. In such a case, the second orsubsequent growth is generally called regrowth.

When the growth of GaN is separated into and carried out in N growthbatches, the crystal growth apparatus and/or the crystal growthconditions used in the n-th growth batch and the (n+1)th growth batchmay be the same or different, where N is an integer of 2 or greater, andn is an integer of from 1 to (N−1). Before the (n+1)th growth batch, acrystal surface formed during the n-th growth batch may be subjected tocleaning including etching.

In one example, by adding a trace amount of oxygen gas (O₂) to a carriergas or by introducing an inert gas added with a trace amount of oxygengas into the second reaction tube 120 together with other gases, grownGaN can be doped with oxygen. Since oxygen (O) acts as a donor in GaNand generates an n-type carrier, GaN doped with oxygen exhibits n-typeconductivity.

2. Use

The GaN crystal production method according to the embodiments may beused for various purposes such as formation of a GaN film for nitridesemiconductor devices and production of bulk GaN crystals.

A nitride semiconductor device is a semiconductor device in which anitride semiconductor is used for a central part of a device structure.Nitride semiconductors are also referred to as, for example,nitride-based Group III-V compound semiconductors, group III nitridecompound semiconductors, and GaN-based semiconductors, and include, inaddition to GaN, a compound in which Ga in GaN is partially or fullysubstituted with another periodic table Group 13 element (such as B, Al,and In). Specific examples of such a compound include AlN, InN, AlGaN,AlInN, GaInN, and AlGaInN.

Specific examples of the nitride semiconductor device include lightemitting devices such as light emitting diodes and laser diodes,electronic devices such as rectifiers, bipolar transistors, field effecttransistors, and HEMTs (High Electron Mobility Transistors),semiconductor sensors such as temperature sensors, pressure sensors,radiation sensors, and visible-ultraviolet light detectors, SAW (SurfaceAcoustic Wave) devices, vibrators, resonators, oscillators, MEMS (MicroElectro Mechanical System) components, voltage actuators, and solarcells.

A bulk GaN crystal produced by the GaN crystal production methodaccording to the embodiments may be used as a material for a GaN wafer(GaN single crystal substrate). That is, by producing a bulk GaN crystalusing the GaN crystal production method according to the embodiments andthen processing the produced bulk GaN crystal, a GaN wafer may beproduced.

Depending on the size of the bulk GaN crystal and the size of the GaNwafer to be produced, a necessary processing may be selected suitablyfrom gliding, lapping, CMP, etching, slicing, coring, a laserprocessing, and the like.

When a bulk GaN crystal has a sufficiently large size, by slicing thebulk GaN crystal in an arbitrary direction, a GaN wafer having anarbitrary surface orientation is obtainable. The obtained GaN wafer maybe a {10-10} wafer, a {30-3-1} wafer, a {20-2-1} wafer, a {30-3-2}wafer, a {10-1-1} wafer, a {30-31} wafer, a {20-21} wafer, a {30-32}wafer, a {10-11} wafer, a (0001) wafer or a (000-1) wafer.

It is noted that a surface orientation attached to a name of a GaN waferis the orientation of a low-index plane which is parallel or nearestparallel to, out of main surfaces of the wafer, the main surface that isfinished to be usable for epitaxial growth. For instance, a GaN waferhaving a (30-3-1) surface which has been brought into an epi-ready stateby a CMP processing is referred to as a {30-3-1} wafer.

An actual main surface of a wafer is often slightly tilted from thelow-index plane attached to the name of the wafer. Such a wafer issometimes referred to as being “off cut”. The angle of the tilt isreferred to as an off-angle, which is usually 5° or less and may be 4°or less, 3° or less, 2° or less, or 1° or less.

Slicing of a bulk GaN crystal may be performed using a wire saw, aninner peripheral blade slicer or the like. Usually, an as-sliced surfaceof a blank wafer obtained by slicing is planarized by mechanicalabrasion (gliding and/or lapping) and then subjected to at least oneprocessing selected from CMP, dry etching, and wet etching to therebyremove a damaged layer formed by the mechanical abrasion on the surface.

A GaN wafer may be preferably used as a substrate for a nitridesemiconductor device. More specifically, by using thin film formingtechnology such as MOCVD, MBE, pulsed vapor deposition, and sputtering,one or more nitride semiconductor thin films may be grown on a GaN waferto form various device structures.

In addition, a GaN wafer may be used as a seed crystal for growing abulk GaN crystal.

3. Experimental Results

In the experiments described hereinafter, a vapor phase growth apparatusof the same type as illustrated in FIGS. 10 and 11 was used. Morespecifically, the apparatus used was a vapor phase growth apparatushaving: a first reaction tube made of quartz and having a first zone anda second zone provided therein; and a second reaction tube made ofquartz and having a growth zone provided therein. As described above,Cl₂ and metal Ga react with each other to generate GaCl in the firstzone, GaCl generated in the first zone reacts with Cl₂ to generate GaCl₃in the second zone, and gaseous gallium chloride including GaCl₃ and NH₃react with each other to generate GaN which is epitaxially grown on aGaN seed crystal in the growth zone.

Hereinafter, when a gas flow rate is mentioned, it means a volumetricflow rate which has been converted into that in a standard state (flowrate represented by a unit such as “sccm”), unless otherwise noted.

Hereinafter, a “first main surface” of a GaN substrate refers to themain surface on which the growth of a GaN crystal was tried or the mainsurface which was used for the growth of a GaN crystal.

3.1. Experiment 1

As seed crystals, nine GaN substrates A to I having different surfaceorientations as shown in Table 1 below were prepared.

All of the GaN substrates A to I were GaN single crystal substrates andfabricated each in the following procedure.

(a) On a C-plane GaN/sapphire template, a bulk GaN crystal was grown byan HVPE method using hydrogen chloride (HCl).

(b) The bulk GaN crystal was sliced with a wire saw to provide anas-sliced substrate having a predetermined surface orientation.

(c) Each main surface of the as-sliced substrate was planarized bymechanical abrasion and then subjected to CMP (Chemical MechanicalPolishing) whereby a damaged layer and scratches formed by themechanical abrasion were removed.

TABLE 1 Surface Angle formed between Direction of orientation normaldirection of intersection line of first main first main surface betweenfirst main surface and [0001] direction surface and C-plane GaN (000-1)180° — substrate A GaN (10-1-1) 118° a-axis direction substrate B GaN(20-2-1) 105° a-axis direction substrate C GaN (30-3-1) 100° a-axisdirection substrate D GaN (10-10)  95° a-axis direction substrate E(off-angled) GaN (30-31)  80° a-axis direction substrate F GaN (20-21) 75° a-axis direction substrate G GaN (10-11)  62° a-axis directionsubstrate H GaN (0001)  0° — substrate I

While Table 1 indicates the surface orientation of the first mainsurface of the GaN substrate E as (10-10) for convenience, the surfaceorientation of the first main surface of the GaN substrate E wasapproximately in the middle of (10-10) and (30-3-1).

Using the above-described vapor phase growth apparatus, it was examinedwhether or not the growth of GaN from GaCl₃ and NH₃ would occur on therespective first main surfaces of the GaN substrates A to I. Theconditions were as shown in Table 2 below, and the growth time was setto 2 hours.

TABLE 2 First zone Carrier gas N₂ Cl₂ partial pressure 2.5 × 10⁻³ atmTemperature 850° C. Second zone Carrier gas N₂ Cl₂ partial pressure 4.8× 10⁻³ atm Temperature 850° C. Growth zone Carrier gas N₂ NH₃ partialpressure 2.0 × 10⁻¹ atm GaCl₃ partial pressure 4.8 × 10⁻³ atm Growthtemperature 1280° C. 

The Cl₂ partial pressure in the first zone shown in Table 2 wascalculated from Formula 1 below.P1(Cl₂)=P1(t)×F1(Cl₂)/{F1(Cl₂)+F1(N₂)}  Formula 1

In the Formula 1,

-   -   P1 (Cl₂) denotes the Cl₂ partial pressure in the first zone,    -   P1 (t) denotes the total pressure (1 atm) in the first zone,    -   F1 (Cl₂) denotes the flow rate of Cl₂ supplied to the first        zone, and    -   F1 (N₂) denotes the flow rate of the carrier gas (N₂) supplied        to the first zone.

The Cl₂ partial pressure in the second zone shown in Table 2 wascalculated from Formula 2 below.P2(Cl₂)=P2(t)×F2(Cl₂)/{F1(N₂)+F2(Cl₂)+F2(N₂)}  Formula 2

In the Formula 2,

-   -   P2 (Cl₂) denotes the Cl₂ partial pressure in the second zone,    -   P2 (t) denotes the total pressure (1 atm) in the second zone,    -   F1 (N₂) denotes the flow rate of the carrier gas (N₂) supplied        to the first zone,    -   F2 (Cl₂) denotes the flow rate of Cl₂ supplied to the second        zone, and    -   F2 (N₂) denotes the flow rate of the carrier gas (N₂) supplied        to the second zone.

In Table 2, it is assumed that the GaCl₃ partial pressure in the growthzone is equal to the Cl₂ partial pressure in the second zone.

The NH₃ partial pressure in the growth zone shown in Table 2 wascalculated from Formula 3 below.PG(NH₃)=PG(t)×FG(NH₃)/{F1(N₂)+F2(Cl₂)+F2(N₂)+FG(NH₃)+FG(N₂)}  Formula 3

In the Formula 3,

-   -   PG (NH₃) denotes the NH₃ partial pressure in the growth zone,    -   PG (t) denotes the total pressure (1 atm) in the growth zone,    -   F1 (N₂) denotes the flow rate of the carrier gas (N₂) supplied        to the first zone,    -   F2 (Cl₂) denotes the flow rate of Cl₂ supplied to the second        zone,    -   F2 (N₂) denotes the flow rate of the carrier gas (N₂) supplied        to the second zone,    -   FG (NH₃) denotes the flow rate of NH₃ supplied to the growth        zone, and    -   FG (N₂) denotes the flow rate of the carrier gas (N₂) supplied        to the growth zone.

At an elapse of growth time of 2 hours, the supply of GaCl₃ to thegrowth zone and heating of the GaN substrate were stopped. After thetemperature of the reaction tube had dropped to room temperature, theGaN substrate was taken out of the vapor phase growth apparatus, and thethickness of the grown GaN layer was examined with a fluorescencemicroscope.

The result showed that for the GaN substrates A to E each having a firstmain surfaces whose normal direction forms an angle of 95° or more withthe [0001] direction of the GaN substrate, GaN layers each having athickness of more than 100 μm were grown on the first main surfaces. Incontrast, for the GaN substrates F to I where the angle was 80° or less,no GaN growth on the first main surface was observed.

Regarding the GaN growth rates calculated from the growth time and thethickness of the GaN layers grown on the respective first main surfaces,while the growth rate was 88 μm/h on the GaN substrate A, the growthrates were higher than 100 μm/h on the GaN substrates B to D and higherthan 200 μm/h on the GaN substrate E. In calculating the growth rate,when the thickness of the GaN layer is not uniform within the layer, themaximum thickness (thickness at a position where the thickness is themaximum) was used.

Measurement of X-ray rocking curves confirmed that the GaN layers grownrespectively on the GaN substrates A to E were single crystal layersformed through epitaxial growth. The X-ray rocking curve measurement wasperformed by using an X-ray diffractometer using CuKα as an X-ray source(the same applies to the measurement of an X-ray rocking curve in otherexperiments).

The results obtained in Experiment 1 are shown summarized in Table 3.

TABLE 3 Thickness Growth Growth of GaN rate of X-ray rocking curve ofGaN layer GaN Reflection FWHM layer (μm) (μm/h) plane (arcsec) GaN Yes175 88 (002) 539 substrate A (102) 595 GaN Yes 280 140 (101) 90substrate B GaN Yes 265 133 (201) 67 substrate C GaN Yes 330 165 (301)112 substrate D GaN Yes 420 210 (100) 235 substrate E GaN No 0 0 —substrate F GaN No 0 0 — substrate G GaN No 0 0 — substrate H GaN No 0 0— substrate I

3.2. Experiment 2

Using the same vapor phase growth apparatus as in Experiment 1, GaN wasgrown on the above-described GaN substrates A to E. Except for thegrowth temperature, the growth conditions were the same as theconditions shown in Table 2 above.

As a result, GaN growth rates on the respective first main surfaces ofthe GaN substrates were as shown in Table 4 below.

TABLE 4 Growth temperature 1230° C. 1280° C. 1330° C. Growth rate GaNsubstrate A 103 88 38 of GaN GaN substrate B 150 140 50 (μm/h) GaNsubstrate C 158 133 153 GaN substrate D 180 165 160 GaN substrate E 194210 240

3.3. Experiment 3

As seed crystals, two types of GaN substrates J and K shown in Table 5below were prepared.

The GaN substrates J and K were GaN single crystal substrates andfabricated in the same manner as the above-described GaN substrates A toI.

The GaN substrate J was a (10-10) substrate (M-plane substrate) havingan off-angle of +10 in the [0001] direction and 3° in the a-axisdirection.

The GaN substrate K was a (10-10) substrate (M-plane substrate) havingan off-angle of +3° in the [0001] direction and 3° in the a-axisdirection.

TABLE 5 Surface Angle formed between Direction of orientation normaldirection of intersection line of first main first main surface betweenfirst main surface and [0001] direction surface and C-plane GaN (10-10)89° +3° in a-axis substrate J (off-angled) direction GaN (10-10) 87° +3°in a-axis substrate K (off-angled) direction

Using the same vapor phase growth apparatus as in Experiment 1, it wasexamined whether or not the growth of GaN from GaCl₃ and NH₃ would occuron the respective first main surfaces of the GaN substrates J and K. Theconditions were as shown in Table 6 below, and the growth time was setto 1 hour.

TABLE 6 First zone Carrier gas N₂ Cl₂ partial pressure 2.1 × 10⁻³ atmTemperature 850° C. Second zone Carrier gas N₂ Cl₂ partial pressure 4.1× 10⁻³ atm Temperature 850° C. Growth zone Carrier gas N₂ NH₃ partialpressure 1.7 × 10⁻¹ atm GaCl₃ partial pressure 4.1 × 10⁻³ atm GrowthTemperature 1230° C. 

The method for calculating the gas partial pressures in the zones shownin Table 6 is the same as that in Experiment 1 above.

At an elapse of growth time of 1 hour, the supply of GaCl₃ to the growthzone and heating of the GaN substrate were stopped. After thetemperature of the reaction tube had dropped to room temperature, theGaN substrate was taken out of the vapor phase growth apparatus, and thethickness of the grown GaN layer was examined with a fluorescencemicroscope.

The result showed that for both of the GaN substrates J and K, GaNlayers each having a thickness of more than 100 μm were grown on thefirst main surfaces.

Measurement of X-ray rocking curves confirmed that the GaN layers grownrespectively on the GaN substrates J and K were single crystal layersformed through epitaxial growth.

The results obtained in Experiment 3 are shown summarized in Table 7.

TABLE 7 Thickness Growth Growth of GaN rate of X-ray rocking curve ofGaN layer GaN Reflection FWHM layer (μm) (μm/h) plane (arcsec) GaN Yes150 150 (100) 152 substrate J GaN Yes 135 135 (100) 84 substrate K

3.4. Experiment 4

Using the same vapor phase growth apparatus as in Experiment 1, GaN wasgrown on the first main surface of each of the above-described GaNsubstrates A and E under four sets of conditions (Conditions 1 to 4)shown in Table 8 below. The four sets of conditions differ in theproduct of the GaCl₃ partial pressure and the NH₃ partial pressure inthe growth zone.

Table 8 also shows growth rates of GaN obtained under each set ofconditions.

TABLE 8 Partial pressures of raw material gases in growth zone (atm)GaCl₃ Growth rate of partial NH₃ partial Growth GaN (μm/h) pressurepressure temperature GaN GaN (i) (ii) (i) * (ii) (° C.) substrate Asubstrate E Condition 1 1.5 × 10⁻³ 6.3 × 10⁻² 9.5 × 10⁻⁵ 1230 6 3Condition 2 1.6 × 10⁻³ 2.0 × 10⁻¹ 3.2 × 10⁻⁴ 1230 30 34 Condition 3 4.1× 10⁻³ 1.7 × 10⁻¹ 7.0 × 10⁻⁴ 1230 81 142 Condition 4 4.9 × 10⁻³ 2.0 ×10⁻¹ 9.8 × 10⁻⁴ 1230 119 195

The results shown in Table 8 are plotted on a graph in FIG. 12. As shownin FIG. 12, the growth rate of GaN was approximately proportional to theproduct of the GaCl₃ partial pressure and the NH₃ partial pressure inthe growth zone, and it was found that the growth rate of GaN iscontrollable by adjusting the partial pressures of raw material gases.

3.5. Experiment 5

Using the same vapor phase growth apparatus as in Experiment 1, GaNlayers were grown from GaCl₃ and NH₃ on the respective first mainsurfaces of five GaN substrates (single crystal substrates) which differin the orientations of the first main surfaces. The growth temperaturewas set to 1280° C. The concentrations of oxygen (O) and silicon (Si)contained in each of the GaN layers grown on the respective GaNsubstrates were measured by SIMS (Secondary Ion Mass Spectroscopy), andthe results are shown in Table 9 below.

TABLE 9 Orientation of Concentrations of impurities in first mainsurface GaN layer grown on GaN substrate of GaN substrate Oxygen(atoms/cm³) Silicon (atoms/cm³) (000-1) 2 × 10¹⁸ 8 × 10¹⁷ (10-1-1) 2 ×10¹⁷ 8 × 10¹⁶ (20-2-1) 3 × 10¹⁷ 2 × 10¹⁷ (30-3-1) 2 × 10¹⁷ 1 × 10¹⁷(10-10) (off-angled) 1 × 10¹⁸ 8 × 10¹⁶

As shown in Table 9, silicon was detected from all the GaN layers. Sinceno silicon was intentionally added, the detected silicon is presumed tobe derived from the material of the reaction tubes, specifically,quartz.

The GaN layers grown on the non-polar or semi-polar GaN surfaces eachhad a silicon concentration of less than 2×10¹⁷ atms/cm³, which was notmore than one fourth of the concentration in the GaN layer grown on the(000-1) surface. This suggests that growth on a non-polar or semi-polarGaN surface is convenient for control of carrier concentration by oxygendoping.

3.6. Experiment 6

As a seed crystal, a GaN substrate L formed of a GaN single crystalgrown by an ammonothermal method was prepared. The GaN substrate L was a(10-10) substrate (M-plane substrate) with an off-angle of +5° in the[0001] direction and had a first main surface whose normal directionforms an angle of 85° with the [0001] direction.

Using the same vapor phase growth apparatus as in Experiment 1, it wasexamined whether or not the growth of GaN would occur on the first mainsurface of the GaN substrate L in the growth zone under the followingconditions: an GaCl₃ partial pressure of 4.8×10⁻³ atm, an NH₃ partialpressure of 2×10⁻¹ atm, and a temperature of 1230° C. As a result, a GaNlayer was grown at a rate of 40 μm/h. Measurement of an X-ray rockingcurve confirmed that the GaN layer was a single crystal layer formedthrough epitaxial growth. The FWHM (Full Width at Half Maximum) of themeasured X-ray rocking curve of the (100) plane was 30 arcsec.

3.7. Experiment 7

As seed crystals, two types of GaN substrates M and N each formed of aGaN single crystal grown by an ammonothermal method were prepared.

The GaN substrate M was a non-off-cut (10-10) substrate (M-planesubstrate) and had a first main surface whose normal direction forms anangle of 90° with the [0001] direction. The GaN substrate N was a(10-10) substrate (M-plane substrate) having an off-angle of −5° in the[0001] direction and had a first main surface whose normal directionforms an angle of 95° with the [0001] direction.

Using the same vapor phase growth apparatus as in Experiment 1, GaN wasgrown on the first main surface of each of the GaN substrates M and Nunder three sets of conditions shown in Table 10 below.

Table 10 also shows results of measurement of GaN growth rates undereach set of conditions and FWHMs of (100) plane X-ray rocking curvesmeasured on the grown GaN layers.

TABLE 10 Partial (100) XRC-FWHM pressures of raw Growth rate of of grownGaN material gases GaN layer in growth zone Growth (μm/h) (arcsec) (atm)temperature GaN GaN GaN GaN GaCl₃ NH₃ (° C.) substrate M substrate Nsubstrate M substrate N Condition 1 4.8 × 10⁻³ 2.0 × 10⁻¹ 1230 225 245252 178 Condition 2 3.4 × 10⁻³ 1.4 × 10⁻¹ 1230 164 194 251 172 Condition3 2.4 × 10⁻³ 1.0 × 10⁻¹ 1230 125 115 74 59

To observe stacking faults, monochromatic CL (CathodoLuminescence)images of the surfaces of the grown GaN layers at a wavelength of 364 nmwere obtained at a temperature of 83 K. Observation of the centralportion of each sample for approximately 5 mm along the C-axis directionshowed that the GaN layer grown on the GaN substrate M under Condition 2or 3 as set out in Table 10 had a surface on which regions crowded withstacking faults existed everywhere, whereas the GaN layer grown on theGaN substrate N under the same Condition 2 or 3 had a surface on whichrelatively few stacking faults existed and regions crowded with stackingfaults existed only partially.

3.8. Experiment 8

As a seed crystal, a GaN substrate O formed of a GaN single crystalgrown by an ammonothermal method was prepared.

The GaN substrate O was a (10-1-1) substrate and had a first mainsurface whose normal direction forms an angle of 118° with the [0001]direction.

Using the same vapor phase growth apparatus as in Experiment 1, GaN wasgrown on the first main surface of the GaN substrate O under three setsof conditions shown in Table 11 below.

Table 11 also shows results of measurement of GaN growth rates under therespective sets of conditions and FWHMs of (101) plane X-ray rockingcurves measured on the grown GaN layers.

TABLE 11 Partial pressures (101) of raw material Growth GaN XRC-FWHMgases in growth zone temper- growth of grown (atm) ature rate GaN layerGaCl₃ NH₃ (° C.) (μm/h) (arcsec) Condition 1 4.8 × 10⁻³ 2.0 × 10⁻¹ 1230275 28 Condition 2 3.4 × 10⁻³ 1.4 × 10⁻¹ 1230 164 36 Condition 3 2.4 ×10⁻³ 1.0 × 10⁻¹ 1230 95 42

Further, (202) X-ray rocking curves of the GaN layer grown on the GaNsubstrate O under Condition 1 as set out in Table 11 were measured byusing an X-ray diffractometer having a higher angular resolution[PANalytical X'Pert Pro MRD manufactured by Spectris Co., Ltd.]. Used asincident optics were a ½° divergence slit, a focusing mirror, a Ge (440)4-crystal monochromator, and a cross slit of w 0.2 mm×h 1 mm. Used asreceiving optics was the OD mode of a semiconductor pixel detector,PIXcel3D®. The optics had an angular resolution of 5 to 6 arcsec.

The beam size of the X-rays on the surface of the GaN layer was set soas to be 0.2 mm×5 mm when the incident angle of the X-rays was 90° (theincident direction of the X-rays was perpendicular to the surface of theGaN layer). At the time of measurement, the direction in which the beamsize was 5 mm was kept perpendicular to the X-ray incidence plane.

First, X-ray rocking curve measurement was carried out at sevenmeasurement points on a straight line passing through an approximatecenter of the surface of the GaN layer and parallel to the a-axis. Thepitch between the measurement points was 1 mm. In each measurement, theX-ray incidence plane was kept parallel to the a-axis. In other words,an ω scan was performed by making X-rays incident on the surface of theGaN layer from a direction perpendicular to the c-axis.

Among the seven measurement points on the straight line parallel to thea-axis, FWHMs of (202) plane X-ray rocking curves had a maximum value of26.8 arcsec, a minimum value of 14.9 arcsec, and a mean value of 18.1arcsec.

Next, the measurement was carried out at seven measurement points on astraight line passing through an approximate center of the surface ofthe GaN layer and perpendicular to the a-axis. The pitch between themeasurement points was 1 mm. In each measurement, the X-ray incidentplane was kept perpendicular to the a-axis. In other words, an a scanwas performed by making X-rays incident on the surface of the GaN layerfrom a direction perpendicular to the a-axis.

Among the seven measurement points located on the straight lineperpendicular to the a-axis, FWHMs of (202) plane X-ray rocking curveshad a maximum value of 18.9 arcsec, a minimum value of 13.3 arcsec, anda mean value of 15.0 arcsec.

3.9. Experiment 9

In Experiment 9, GaN substrates P and Q were prepared to examine whetherSAG (Selective Area Growth) of a GaN crystal using GaCl₃ and NH₃ as rawmaterials is feasible or not. The GaN substrate P had a pattern maskarranged on the first main surface of a (000-1) substrate equivalent inquality to the above-described GaN substrate A, while the GaN substrateQ had a pattern mask arranged on the first main surface of a (10-10)substrate, with an off-angle of −5° in the [0001] direction, equivalentin quality to the above-described GaN substrate E.

The pattern masks arranged on the respective first main surfaces of theGaN substrates P and Q were formed as follows: after deposition of 80nm-thick SiN_(x) thin film by a plasma CVD method, circular openingseach with a diameter of 5 μm and arranged at a pitch of 10 μm in aclosest packed manner were provided in the thin film by usingconventional photolithography and etching technique.

Using the same vapor phase growth apparatus as in Experiment 1, GaN weregrown from GaCl₃ and NH₃ on the respective first main surfaces of theGaN substrates P and Q. The GaCl₃ partial pressure and the NH₃ partialpressure in the growth zone were set to 2.2×10⁻³ atm and 9.0×10⁻² atm,respectively. Two different growth temperatures of 1050° C. and 1230° C.were used.

As a result, SAG was observed on both of the GaN substrates P and Q andat both growth temperatures. Specifically, as a result of brief growth,GaN islands were formed over the circular openings in the pattern masks.

A planar SEM image and a bird's-eye SEM image of a GaN island formed bySAG on the GaN substrate P at a growth temperature of 1050° C. areillustrated in FIG. 13A and FIG. 13B, respectively.

A planar SEM image and a bird's-eye SEM image of a GaN island formed bySAG on the GaN substrate P at a growth temperature of 1230° C. areillustrated in FIG. 14A and FIG. 14B, respectively.

A planar SEM image and a bird's-eye SEM image of a GaN island formed bySAG on the GaN substrate Q at a growth temperature of 1050° C. areillustrated in FIG. 15A and FIG. 15B, respectively.

A planar SEM image and a bird's-eye SEM image of a GaN island formed bySAG on the GaN substrate Q at a growth temperature of 1230° C. areillustrated in FIG. 16A and FIG. 16B, respectively.

As shown in FIGS. 13A, 13B, 15A and 15B, on the surfaces of the GaNislands formed at a temperature of 1050° C., clear (000-1) facets and{10-10} facets appeared, whereas neither a {11-20} facet nor a {hkil}facet where l>0 was observed. Here, a {hkil} facet where l>0 is a facetwhose normal direction forms an angle of less than 90° with the [0001]direction, which includes a (0001) facet.

As shown in FIGS. 13A and 13B, the GaN islands grown on the GaNsubstrate P each had an upper portion in a shape of a hexagonal prismterminating with a flat top surface, and the top surface was a (000-1)facet while the side surfaces of the hexagonal prism were {10-11}facets. The orientation of the top surface was confirmed by examiningwhether the top surface was etched with KOH or not. It is known that inGaN, a (0001) surface is not substantially etched with KOH, whereas a(000-1) surface is easily etched with KOH.

As shown in FIGS. 14A, 14B, 16A and 16B, on the surfaces of the GaNislands grown at a temperature of 1230° C., clear (000-1) facets,{10-1-1} facets, and {10-10} facets appeared, whereas neither a {11-20}facet nor a {hkil} facet where l>0 was observed.

As shown in FIGS. 14A and 14B, the GaN islands grown on the GaNsubstrate P each had an upper portion in a shape of a hexagonal prismterminating with a flat top surface, and the top surface was a (000-1)facet while the side surfaces of the hexagonal prism were {10-10}facets. Between the (000-1) facet and each of the {10-10} facets, a{10-1-1} facet was formed as a chamfer.

The GaN islands formed as a result of SAG over the openings of thepattern masks each had a shape called quasi-equilibrium crystal shape,and the facets appearing on the surfaces of the GaN islands indicatestable faces in the growth system of a GaN crystal from GaCl₃ and NH₃.Even when a bulk GaN crystal grows from GaCl₃ and NH₃, the facetsobserved on the GaN islands are predicted to appear on the surfaces ofthe bulk GaN crystal.

When the GaN crystals were allowed to continue growing on the GaNsubstrates P and Q after the GaN islands had been formed, regardless ofwhether at a temperature of 1050° C. or 1230° C., coalescence betweenthe GaN islands occurred, and GaN layers each covering the entire firstmain surface of the substrate were formed. Regardless of whether on theGaN substrate P or on the GaN substrate Q, the formed GaN layers eachhad a top surface with high flatness.

For comparison, GaN crystals were grown on the GaN substrates P and Qusing the same vapor phase growth apparatus as in the above-describedexperiments but under the condition without any supply of Cl₂ to thesecond zone. When no Cl₂ is supplied to the second zone, GaCl issubstantially the only source of Ga to be supplied to the growth zone.SEM images of GaN islands formed under such a condition as a result ofbrief growth on the substrates are illustrated in FIGS. 17A, 17B, 18Aand 18B.

FIGS. 17A and 17B illustrate bird's-eye SEM images of the GaN islandsgrown at a temperature of 1050° C., where FIG. 17A illustrates theisland grown on the GaN substrate P, while FIG. 17B illustrate theislands grown on the GaN substrate Q.

As shown in FIG. 17A, no clear facet was observed on the surfaces of theGaN islands grown at a temperature of 1050° C. on the GaN substrate Pfrom GaCl and NH₃.

On the other hand, as shown in FIG. 17B, on the surfaces of the GaNislands grown at a temperature of 1050° C. on the GaN substrate Q fromGaCl and NH₃, in addition to (000-1) facets, {10-1-1} facets, and{10-10} facets, {10-11} facets were also observed.

FIGS. 18A and 18B illustrate bird's-eye SEM images of the GaN islandsgrown at a temperature of 1230° C., where FIG. 18A illustrates theisland grown on the GaN substrate P, while FIG. 18B illustrates theisland grown on the GaN substrate Q.

As shown in FIGS. 18A and 18B, regardless of whether on the GaNsubstrate P or on the GaN substrate Q, on the surfaces of the GaNislands grown at a temperature of 1230° C. from GaCl and NH₃, only(000-1) facets appeared, and neither a non-polar {10-10} facet nor asemi-polar {10-1-1} facet was observed.

Although the present invention has been specifically described withreference to the embodiments as above, each embodiment was presented asan example and does not limit the scope of the present invention. Eachof the embodiments described herein can be variously modified within thescope not departing from the spirit of the present invention, and can becombined with any feature described in other embodiments as long as sucha combination can be carried out.

REFERENCE SIGNS LIST

-   -   10 GaN Substrate    -   11 first main surface    -   12 second main surface    -   13 side surface    -   100 vapor phase growth apparatus    -   110 first reaction tube    -   111 first Cl₂ supply port    -   112 second Cl₂ supply port    -   113 gas outlet    -   114 funnel-shaped tube    -   115 baffle    -   120 second reaction tube    -   121 NH₃ supply port    -   122 exhaust port    -   130 susceptor    -   Z1 first zone    -   Z2 second zone    -   Z3 growth zone

What is claimed is:
 1. A method for producing a GaN crystal, comprising:(i) a seed crystal preparation step of preparing a GaN seed crystalhaving a non-polar or semi-polar surface whose normal direction forms anangle of 85° or more and less than 170° with a [0001] direction of theGaN seed crystal; and (ii) a growth step of growing GaN from GaCl₃ andNH₃ via a vapor phase epitaxy method on the non-polar or semi-polarsurface of the GaN seed crystal, wherein a row-index orientation of theGaN seed crystal parallel or nearest parallel to the normal of thenon-polar or semi-polar surface is <10-10>, <30-3-1>, <20-2-1>,<30-3-2>, or <10-1-1>.
 2. The method for producing a GaN crystalaccording to claim 1, wherein the angle formed by the normal directionof the non-polar or semi-polar surface with the [0001] direction of theGaN seed crystal is in a range of 85° or more and less than 132°.
 3. Themethod for producing a GaN crystal according to claim 1, wherein theangle formed by the normal direction of the non-polar or semi-polarsurface with the [0001] direction of the GaN seed crystal is 87° or lessor 93° or more.
 4. The method for producing a GaN crystal according toclaim 1, wherein in the growth step, GaN is grown on the non-polar orsemi-polar surface at a growth rate of 1 μm/h or more.
 5. The method forproducing a GaN crystal according to claim 4, wherein the growth rate is50 μm/h or more.
 6. The method for producing a GaN crystal according toclaim 4, wherein the growth rate is less than 150 μm/h.
 7. The methodfor producing a GaN crystal according to claim 1, wherein in the growthstep, GaCl₃ is supplied to the GaN seed crystal at a partial pressure of1.5×10⁻³ atm or more.
 8. The method for producing a GaN crystalaccording to claim 1, wherein in the growth step, a product of partialpressures of GaCl₃ and NH₃ supplied to the GaN seed crystal is 9.5×10⁻⁵atm² or more.
 9. The method for producing a GaN crystal according toclaim 1, wherein an intersection line between the non-polar orsemi-polar surface and a C-plane of the GaN seed crystal extends in ana-axis direction ±15°.
 10. The method for producing a GaN crystalaccording to claim 9, wherein the intersection line extends in an a-axisdirection ±3°.
 11. The method for producing a GaN crystal according toclaim 1, wherein the GaN seed crystal is at least part of a GaNsubstrate, and the non-polar or semi-polar surface is a main surface ofthe GaN substrate.
 12. The method for producing a GaN crystal accordingto claim 11, wherein the GaN substrate is a GaN single crystalsubstrate.
 13. The method for producing a GaN crystal according to claim11, wherein the GaN substrate is a template substrate comprising a basesubstrate and a GaN single crystal layer grown on the base substrate.14. The method for producing a GaN crystal according to claim 11,wherein the GaN substrate is a GaN layer-bonded substrate comprising abase substrate and a GaN single crystal layer bonded to the basesubstrate.
 15. The method for producing a GaN crystal according to claim11, wherein in the growth step, a bulk GaN crystal grows on thenon-polar or semi-polar surface to a maximum growth height, the maximumgrowth height is in a range of 300 μm or more.
 16. The method forproducing a GaN crystal according to claim 15, wherein the maximumgrowth height of the bulk GaN crystal is in a range of 300 μm or moreand less than 200 mm.
 17. The method for producing a GaN crystalaccording to claim 1, wherein in the growth step, growth of GaN isrepeated intermittently.
 18. The method for producing a GaN crystalaccording to claim 1, wherein the GaCl₃ is generated by reacting metalGa and Cl₂ with each other to produce GaCl and reacting the producedGaCl with Cl₂.
 19. The method for producing a GaN crystal according toclaim 1, wherein in the growth step, GaN is grown at a growthtemperature of 1200° C. or more.